1. Field of the Invention
The present invention relates generally to a recording apparatus that forms images such as, for example, characters on a recording material on which the images are to be formed such as paper, a plastic, a sheet, cloth, an article, or the like. The present invention also relates to a recording head used in the recording apparatus, a recording head substrate, and a heating resistor.
2. Related Background Art
An ink jet recording apparatus records high-definition images by discharging ink as minute droplets from a discharge port onto a recording material. The ink jet recording apparatus converts electric energy to heat energy and generates air bubbles in the ink using the heat energy. The force exerted by the air bubbles allows the droplets to be ejected from the discharge port located at the tip of an ink jet recording head. The droplets ejected from the discharge port adhere onto the recording material and thereby images are recorded. Generally, the ink jet recording head used in such an ink jet recording apparatus has a heating resistor that converts electric energy to heat energy.
The heating resistor is a thermal converter that converts electric energy to heat energy to be generated. The heating resistor is protected with an upper protective layer so as not to come into contact with ink.
FIG. 5 is a sectional view of a substrate for an ink jet recording head. With reference to FIG. 5, an SiO2 interlayer film 52 is disposed on an Si substrate 51, and a heating resistor 53 made of TaSiN or the like is formed on the interlayer film 52. An Al wire 54 is provided on the heating resistor 53, but there is a region where the wire 54 is not formed on the heating resistor 53. This region serves as a portion 57 on which heat acts (hereinafter referred to as a heat acting portion 57). In addition, there is provided a protective layer 55 for protecting the heating resistor 53 and the wire 54 from ink penetration or the like. In the heat acting portion 57, a Ta anticavitation film 56 for protecting the protective layer 55 from chemical and physical damages accompanying heat generation is disposed on the protective layer 55.
The current flowing in the wire 54 flows into the heating resistor 53 in the heat acting portion 57 and thereby the electric energy is converted into heat energy. Then the heat energy allows the recording head to discharge ink onto the recording material. In order to record a desired image on the recording material, ON-OFF switching of the current flowing into the heating resistor 53 controls the discharge of ink. Hence, pulsed currents are applied to the heating resistor 53 repetitively.
When it is tried to record images at high speed, which is a natural requirement for recording apparatuses, it is necessary to increase the frequency of the pulsed current, i.e. the drive frequency of the heating resistor 53. Furthermore, in order to improve image quality, the amount of ink to be discharged per dot must be reduced. When it is tried to maintain a high recording speed and to achieve a reduction in size of the heating resistor 53 at the same time, the increase in the drive frequency is required.
Repetitive applications of pulsed currents change the resistance value of the heating resistor 53 and eventually cause breaking of wire. It is assumed that the change in resistance value of the heating resistor 53 is caused by crystallization and a surface oxidation reaction. When the resistance value of the heating resistor 53 changes, the heat energy generated therein changes. When the heat energy used for ink discharge becomes too low, ink is not discharged from the discharge port. Furthermore, when the heat energy becomes too high, ink is spattered over a broad area of the recording material and thereby normal images cannot be recorded. This is so-called “uneven printing”. Hence, the heating resistor 53 is required to have durability to the repetitive pulse applications.
Heating resistors with a relatively low resistance value, which have a sheet resistance of about 25 Ω/□ to 50 Ω/□, are used as conventional heating resistors. It has been studied to use heating resistors with a high resistance value of about 200 Ω/□ to 400 Ω/□ so as to reduce power consumption in the recording apparatus without decreasing the heat energy generated therein.
For instance, Japanese Patent Application Laid-Open No. 10-114071 discloses an ink jet recording head with a heating resistor made of TaSiN, TaSiO, or TaSiC having a specific resistance value of 4000 μΩ·cm or less. In addition, it describes, for example, a method for forming a TaSiN heating resistor with a thickness of 100 nm having a sheet resistance of 270 Ω/□ by reactive sputtering.
The conventional heating resistor described in Japanese Patent Application Laid-Open No. 10-114071 has a resistivity change ratio of about 1.0 to 3.0% when the number of repetitive pulse applications is set to 3.0×108 and has durability to an extent that allows no breaking of wire to be caused when the number of repetitive pulse applications is set to 5.0×109 in a durability test with respect to the repetitive pulse applications. Here, the “resistivity change ratio” denotes the rate of change of resistance value after the repetitive pulse applications with respect to that before the repetitive pulse applications. The resistivity change ratio is expressed by (A′−A)/A, wherein A and A′ denote the resistances before and after the pulse applications, respectively.
The heating resistor is used not only for an ink jet recording head but also for a thermal head for recording images by being brought into direct contact with heat sensitive paper or an ink ribbon.
The need for high durability of heating resistors is increasing more and more. At present, durability is required that allows a heating resistor to withstand pulse applications repeated about 1.0×109 times. In order to avoid the conditions where ink is not discharged or uneven printing occurs, a resistivity change ratio of 5.0% or lower is required. Hence, it is necessary to meet the above-mentioned requirement in a heating resistor having a high resistance value of about 200 Ω/□ to 400 Ω/□.